The invention relates to a method for producing a solid body including a microstructure, especially, a semiconductor element, wherein the surface of a substrate is provided with a masking layer which is impermeable to a substance to be applied, and wherein the substance is subsequently incorporated into substrate regions not covered by the masking layer.
A process of this type is known from the book Integrierte Digitalbausteine [Integrated Digital Components], Siemens AG (1970), pages 12 and 13. According to this process, to produce a semiconductor element, a surface region of a silicon substrate is covered by a masking layer which consists of silicon dioxide and is impermeable to a dopant, while other surface regions remain exposed. To create the masking layer, the substrate is first placed in a stream of oxygen where a continuous silicon dioxide layer is formed on the surface of the substrate. A light-sensitive photoresist is then applied to the substrate surface. This photoresist is exposed through a photomask which transmits light at those sites at which the substrate is to remain exposed for doping. After exposure, the photoresist is removed with a solvent from the exposed sites, while the unexposed regions of the photoresist which are insoluble by the solvent remain on the substrate. An etching agent is then used to etch away the silicon dioxide from the resist-free sites, after which the remaining photoresist is removed. The substrate is then exposed at a temperature of approximately 1000° C. to a gas phase containing the dopant, during which the dopant diffuses into the open substrate sites not covered by the silicon dioxide. When the substrate cools, the diffusion process ceases. The substrate has then been doped regionally at the intended sites. The method may be used, for example, to integrate transistors, diodes, or electronic functional elements in the substrate.
The previously known method has the disadvantage, however, that the costs of the exposure device required to expose the substrate increase significantly as the size of the microstructures to be produced decrease—see F&M, Volume 107 (1994), Number 4, pages 57–60, and Number 9, pages 40–44. A principal disadvantageous aspect is that the resolution of the exposure device must be dimensioned for the smallest structure to be produced on the substrate even when large structures are simultaneously generated on the substrate. The production of solid bodies with the smallest structures is therefore complex and expensive.
European Patent 0 412 263 A2 describes a method for producing a via hole in an integrated semiconductor circuit in which according to the method, a mask is used to dope a semiconductor body, and then oxidize the surface of the semiconductor body, thereby creating an oxidation layer which is thicker in the doped semiconductor regions than in the undoped semiconductor regions. An etching process is then used to remove the thinner section of the oxidation layer so as to be able to contact the semiconductor body. IBM Technical Disclosure Bulletin, Volume 27, No. 11, April 1985, pages 6533–6536 discloses an analogous method for producing an insulation layer including regionally thinner sections on a semiconductor body, wherein the semiconductor body is doped through these thinner sections of the insulation layer.
Japanese Patent 02 077135 (Patent Abstracts of Japan) discloses a method in which a gate oxide layer is applied to a silicon substrate. Polysilicon is deposited and structured on this gate oxide layer, a base layer being produced as a mask using the structured polysilicon. A nitride layer is then deposited and structured, a source layer being produced as a mask using the nitride layer. A thick oxide layer is subsequently produced by selective oxidation and the nitride layer is removed, so that a highly doped layer is produced as a mask using the thick oxide layer. An intermediate layer is then deposited, thereby producing a via hole and an electrode.
U.S. Pat. No. 5,171,705 describes a method for producing a DMOS transistor in which a self-adjusting body connection contact is produced.
There is a need for a method which provides inexpensive production of a solid body with a small structure.